1. Field of the Invention
The present invention relates to a control apparatus for a multi-air-conditioner system for controlling the operation of a multi-air-conditioner system.
2. Description of the Background Art
An example of the structure of a general cooling cycle in a multi-air-conditioner system is shown in FIG. 7. The multi-air-conditioner system shown in FIG. 7 can selectively perform either a cooling operation or a heating operation upon switching of a four-way valve 74.
In the cooling operation, refrigerant is supplied to a plurality of multi-controllers 70a and 70b via a passage from compressors 76a and 76b, to oil separators 81a and 81b, check valves 82a and 82b, a four-way valve 74, an outdoor heat exchanger 77, a check valve 83, a liquid tank 84, and to a header 85a. The refrigerant supplied to the multi-controller 70a for example is distributed to three indoor units 71a to 71c via control valves 73a to 73c and expansion valves 72a to 72c. Each indoor unit is constructed substantially of an indoor heat exchanger. The refrigerant performs heat-exchange with the room air while passing through the indoor units 71a to 71c, and is collected again at a second header 85b. The refrigerant supplied from the header 85a to the second multi-controller 70b and passed through indoor units 71d to 71f is also collected at the second header 85b. The refrigerant at the second header 85b returns via the four-way valve 74 and an accumulator 75 to the suction side of the compressors 76a and 76b.
In a heating operation which is conducted upon switching the four-way valve 74, the refrigerant supplied from the compressors 76a and 76b and passed through the four-way valve 74 is first introduced to the header 85b. and diverted into the multi-controllers 70a and 70b. The refrigerant then passes through the indoor units 71a to 71c and 71d to 71f, again passes through the multi-controllers 70a and 70b, and is collected at the header 85a. Specifically, within the multi-controller 70a, the refrigerant passed through the indoor heat exchangers 71a to 71c flows toward the header 85a via the check valves 88a to 88c and control valves 73a to 73c. The refrigerant from the header 85a is re-circulated to the compressors 76a and 76b via the liquid tank 84, expansion valve 78, indoor heat exchanger 77, four-way valve 74 and accumulator 75.
If an operation command is given to the indoor unit group 71, e.g., the indoor unit 71a shown in FIG. 7, the control valve 73a is opened and the other control valves 73b and 73c are maintained closed.
An apparatus for controlling the above-described cooling cycle is shown in FIG. 6. As shown in FIG. 6, each indoor unit 71a to 71c has its own terminal console 61a to 61c. A command from the terminal consoles 61a to 61c is sent via indoor microcomputers 62a to 62c to a multi-controller 63a. Upon input of an operation command from the terminal console 61a for example, the multi-controller 63a outputs an open command to the control valve 73a belonging to the indoor unit 71a. In addition, the multi-controller 63a causes inverters 65a and 65b, via an interface unit (I/F unit) 64, 65b to be driven. The inverters 65a and 65b supply power to AC motors (not shown) which drive the compressors 76a and 76b.
A command from terminal consoles 61d to 61f is sent to the I/F unit 64 via indoor microcomputers 62d to 62f and multi-controller 63b.
With a conventional control apparatus for a multi-air-conditioner system, if the indoor unit group 71 is partially operated, e.g., only the indoor unit 71a is operated, the corresponding control valve 73a is opened and the other control valves 73b and 73c are closed for the indoor units 71b and 71c now at a stop. Such an open/close state of the control valves also occurs during a so-called "thermo-off". Namely, a thermostat is actuated when the room temperature becomes equal to or lower than a preset temperature during a cooling operation, or when the room temperature becomes equal to or higher than a preset temperature during heating operation. Upon actuation of the thermostat, the corresponding control valve is closed. In such a case, refrigerant containing lubricating oil which has leaked from the compressor and has not been recovered by the oil separators 81a and 81b remains in the indoor unit whose operation is being intercepted. If the refrigerant containing lubricating oil remains in the indoor unit for which operation is being intercepted, the amount of lubricating oil in the compressors 76a and 76b is gradually reduced and also the amount of refrigerant recirculating to the compressors 76a and 76b is reduced. Reduction o lubricating oil results in lowering the level of oil in the compressor, and may cause abnormal lubrication. Furthermore, deficiency of refrigerant results in a pressure rise of the compressor. Therefore, it has been necessary in such a case to forcibly lower the capability of the cooling cycle by stopping a room fan or by reducing the speed of the compressor.